PolymerChemistry_ⅡBTEC-C吴倩莹.doc

Guangdong Institute of EducationBTEC CenterProgram: HND in Applied Chemistry Unit Title: Polymer Chemistry Unit No: 16 Assignment Title: The basic properties and environmental behaviour of polymers Issue Date: May 10, 2011 Submission Deadline: June 20, 2011 Assessor/Tutor: Qiangfang He and Hongming Wang Internal Verifier: Wei Yin Student:Qianying Wu Students Reg. No: B876546 NOTES TO STUDENTSl Check carefully the submission date and the instructions given with the assignment. Late assignments will not be accepted.l Ensure that you give yourself enough time to complete the assignment by the due date.l You must take responsibility for managing your own time effectively.l If you are unable to hand in your assignment on time and have valid reasons such as illness, you may apply (in writing) for an extension. l Failure to achieve a PASS grade will results in a REFERRAL grade being given.l Take great care that if you use other peoples work or ideas in your assignment, you properly reference them in your text and any bibliography.l When you refer to the work of other authors in your assignment, you must practice citation by following Harvard System for Referencing.l If you are caught plagiarizing, you could have your grade reduced to zero, or at worst, you could be excluded from the course.STUDENTS DECLARATION:I confirm that this is all my own work.Student Signature: Qianying Wu ASSESSMENTOutcome/SkillCriteriaEvidenceFeedbackAssessPass AssessmentP16.2 Deduce basic properties of polymers from their structural featuresP16.2.1 deduce the glass transition temperature of polymers using their structural features Deduce the relationships between the glass transition temperature and structure of polymers P16.2.2 relate basic properties of polymers to their glass transition temperatures (strength, stiffness and impact strength)Relate the effect of glass transition temperatures on strength, stiffness and impact strength of polymersP16.2.3 deduce the ability of a polymer to crystallise from its structural features Deduce the relationships between structural regularity and crystallisability P16.2.4 relate crystal structure to applications of polymersRelate the effect of crystallinity on the properties of polymersP16.2.5 calculate molecular mass averages and molecular mass distribution and relate the findings to mechanical properties and processing behaviour Calculate the number-average molecular weight, weight-average molecular weight, PDI of the polystyrene and relate the findings to mechanical properties and processing behaviourP16.3. Investigate service performance and environmental behaviour of polymersP16.3.1 identify the degradative influences on natural rubber and polypropene Identify the influencing factors of degradation, i.e. thermal degradation, mechanical degradation etc. P16.3.2 identify and describe the action of typical commercial antidegradants for these polymers Identify and describe the action of typical commercial antidegradants for these polymers, e.g. the protection of polymers from photo oxidation etc.P16.3.3 explain the potential environmental stress cracking of a range of polymersExplain the potential environmental stress cracking of a range of polymersAdvanced GradingM1 identify and apply strategies to find appropriate solutionsM1.1 effective judgements have been made.M1.2 complex problems with more than one variable have been exploredM1.3 an effective approach to study and research has been appliedM1.1 effective judgements have been made.M1.2 complex problems with more than one variable have been exploredM1.3 an effective approach to study and research has been applied M2 select/design and apply appropriate methods/techniquesM2.1 relevant theories and techniques have been applied.M2.2 a range of methods and techniques have been applied.M2.3 a range of sources of information has been used.M2.4 the selection of methods and techniques/sources has been justified.M2.6 complex information/data has been synthesised andProcessed.M2.7 appropriate learning methods/techniques have been applied.M2.1 relevant theories and techniques have been applied.M2.2 a range of methods and techniques have been applied.M2.3 a range of sources of information has been used.M2.4 the selection of methods and techniques/sources has been justified.M2.7 appropriate learning methods/techniques have been applied.M3 present and communicate appropriate findingsM3.1 the appropriate structure and approach has been used.M3.2 coherent, logical development of principles/concepts for the intended audience.M3.3 a range of methods of presentation have been used and technical language has been accurately used.M3.4 communication has taken place in familiar and unfamiliar contexts.M3.5 the communication is appropriate for familiar and unfamiliar audiences and appropriate media have been used.M3.1 the appropriate structure and approach has been used.M3.2 coherent, logical development of principles/concepts for the intended audience.M3.3 a range of methods of presentation have been used and technical language has been accurately used.M3.4 communication has taken place in familiar and unfamiliar contexts.D1 use critical reflection to evaluate own work and justify valid conclusionsD1.1 conclusions have been arrived at through synthesis of ideas and have been justified.D1.2 the validity of results has been evaluated using defined criteria.D1.3 self-criticism of approach has taken place.D1.4 realistic improvements have been proposed against defined characteristics for success.D1.1 conclusions have been arrived at through synthesis of ideas and have been justified.D1.2 the validity of results has been evaluated using defined criteria.D1.3 self-criticism of approach has taken place.D2 take responsibility for managing and organising activitiesD2.1 autonomy or independence has been demonstrated.D2.2 substantial activities, projects or investigations have been planned, managed and organised.D2.3 activities have been managed.D2.4 the unforeseen has been accommodated.D2.5 the importance of interdependence has been recognized and achieved.D2.1 autonomy or independence has been demonstrated.D2.2 substantial activities, projects or investigations have been planned, managed and organised.D3 demonstrateconvergent/lateral/ creative thinkingD3.1 ideas have been generated and decisions taken.D3.2 self-evaluation has taken place.D3.3 convergent and lateral thinking have been applied.D3.4 problems have been solved.D3.5 innovation and creative thought have been applied.D3.6 receptiveness to new ideas is evident.D3.7 effective thinking has taken place in unfamiliar contexts.D3.1 ideas have been generated and decisions taken.D3.3 convergent and lateral thinking have been applied.D3.4 problems have been solved. Assessors signature: Hongming WangIV agreement: Yes No IV signature: Students Feedback Students signature: Qianying WuNotes:Assignment DescriptionScenarioThe glass transition temperature is an important parameter of a polymeric material. It is used as a measure for evaluating the flexibility of a polymer molecule and the type of response the polymeric material would exhibit to mechanical stress. The Tg value helps in choosing the right processing temperature, i.e., the temperature region in which the material can be converted into finished products through different processing techniques. The properties of a polymer such as density, modulus, hardness, permeability and heat capacity will be largely affected by its crystallinity. Whether a polymer can crystallise or not depends ,apart from its structural regularity, on many other factors. A polymer degradation is characterized by an uncontrolled change in the molecular weight or constitution of the polymer. Conventionally, the term degradation is taken to mean a reduction in the molecular weight of the polymer. A polymer can suffer degradation mainly at two stages of its life. First, during the fabrication process and secondly, during its daily usage. In this paper, you are to deduce basic properties of polymers from their structural features and investigate service performance and environmental behaviour of polymers. To achieve the assessment criteria for pass (P16) you must demonstrate the ability to:l Deduce basic properties of polymers from their structural featuresl Investigate service performance and environmental behaviour of polymers.Tasks1. Deduce the glass transition temperature of polymers using their structural features.2. Relate basic properties of polymers to their glass transition temperatures (strength, stiffness and impact strength).3. Deduce the ability of a polymer to crystallise from its structural features.4. Relate crystal structure to applications of polymers.5. Calculate molecular mass averages and molecular mass distribution and relate the findings to mechanical properties and processing behaviour.6. Identify the degradative influences on natural rubber and polypropene.7. Identify and describe the action of typical commercial antidegradants for these polymers.8. Explain the potential environmental stress cracking of a range of polymers.The basic properties and environmental behaviour of polymersAuthor name: Qianying WuLearner Code: B876546Abstract: The article mainly introducedthe knowledge of the glasstransition temperaturepolymers(OF),crystalline polymers and environmenteffectson the polymer.Keywords: polymer、glass transition、Crystallization、polypropene、natural rubber1 Basic properties of polymers 1.1 The glass transition temperature of polymersP16.2.1 deduce the glass transition temperature of polymers using their structural features. Glasses (either organic polymers or inorganic glasses based on SiO2) have a volume-temperature curve like that shown below. Above Tm, the melting point, the chains are fluid. At Tm, they would like to crystallize, since the crystalline form has lower molar volume (higher density), but cant find the right orientation. At the glass transition temperature Tg, the chains become frozen into a glass. Between Tm and Tg, the polymer is a metastable viscous liquid, in which the chains can undergo segmental motion. In the macroscopic sense, the polymer will be elastomeric above Tg and stiff below Tg. Note that the thermal behavior of a glass-forming liquid depends on the cooling rate, and that there is a range of temperature (centered about Tg) where the glass can be formed.Fig.1 There is a relation between the ease of chain rotation (controlling conformation) and the locked-in configuration of polymer backbone chains. It is most easily appreciated by examining the effect of different backbone configurations on the glass-transition temperature or Tg. As the temperature decreases, there must come a point when all rotation about chain bonds ceases entirely. The temperature at which chain molecular rotation ceases is the glass transition temperature, because the chains can no longer respond to external strain by uncoiling and lengthening by chain rotation. In other words, the polymer becomes glassy and rigid. For polyethylene, the Tg is very low and occurs at about 90 C. On the other hand, if ways of hindering chain rotation are used, for example by increasing the physical size of pendant groups, then the Tg would be expected to increase. Thus polypropylene with a large methyl group on every alternate chain atom has a Tg of about 5 C.P16.2.2 relate basic properties of polymers to their glass transition temperatures (strength, stiffness and impact strength) There are several factors that influence the value of Tg, and determine therefore the temperature range over which a polymer will be elastomeric or brittle. One of the most imporant is the flexibility of the polymer backbone, since chain motions generally require flexing of the backbone and rotation about intrachain bonds. For example, the silicone polymers, of which poly(dimethylsiloxane) is an example, have very low Tg values (in this case -123oC) because the Si-O-Si linkage is very flexible and deformable. This polymer happens to be what Silly Putty is made of. Benzene rings either in the side-groups or the backbone have a stiffening effect on the polymer, and increase Tg. For this reason, polystyrene (Styrofoam, Tg = 100oC) and polyethylene terephthalate (Dacron, Tg = 70oC) are rather stiff, glassy polymers. Intrachain forces - covalent and non-covalent. One of the most important factors controlling polymer properties are the forces between polymer chains. We have seen that covalent crosslinking makes a thermoplastic polymer into a thermoset one. With light crosslinking the polymer is rubbery and flexible, but with heavy crosslinking it is stiff, like an epoxy resin or cured silicone. In viscoelastic materials, the presence of liquid-like behavior depends on the properties of and so varies with rate of applied load, i.e., how quickly a force is applied. And about stiffness versus temperature,on cooling, rubber undergoes a liquid-glass transition, which has also been called a rubber-glass transition.1.2 Crystallization of pomersP16.2.3 deduce the ability of a polymer to crystallise from its structural features We know that small molecules like to form crystalline solids when they get cold. Long polymer chains can have a hard time crystallizing, however, since the individual chains get tangled up and need to untangle to make a regular crystalline array. This is particularly true if the polymer melt is very viscous, or if there are substituents on the chain that do not pack very well in the solid state. Crystalline polymers usually contain regions of well-packed chains separated by amorphous (liquid-like) regions. Pulling a fiber of a linear polymer causes the chains to line up, and can induce crystallization. This phenomenon occurs, for example, when you pull slowly on a polyethylene sixpack harness (the polymer necks down and becomes much harder to break, because the chains align along the pulling direction). Snapping the plastic abruptly apart (before stretching it) is easier, because the chains dont have time to orient. Besides viscosity, there are other factors that influence the ability of a polymer to crystallize. One of them is the nature of the side groups on the polymer chains. With very bulky side groups, or side groups that vary in an irregular way, the chains have a hard time organizing into an ordered, crystalline solid. This effect is important, because crystalline polymers tend to be much stiffer, harder, and more dense than amorphous polymers. P16.2.4 relate crystal structure to applications of polymers Crystallinity of polymersallowsthe polymer chainarranged in neat rows,and let themclosely,thuscan enhancethe force betweenthe molecularchains. That the density,strength, hardness,heat resistance, solvent resistance, chemical resistanceand other properties in polymercan be improved, thereby improving theperformanceof plastics. But thecrystallinity of polymerswill reduce thehigh elasticity, elongation, impact resistance,strength and other performance hit, which is not conducivetothe material mainperformance in flexibility, toughness. For example, it can make rubberloses its elasticity, burst occurred. 1.3 Molecular mass averages and molecular mass distribution A polydisperse sample of polystyrene is prepared by mixing three monodisperse samples in the following proportions:1-3 g 10,000 molecular weight 1-4 g 50,000 molecular weight1-5 g 100,000 molecular weightUsing this information, calculate the number-average molecular weight, weight-average molecular weight, and PDI of the mixture.Solve:P16.2.5 relate the findings to mechanical properties and processing behaviour Many commercially useful polymers are selected on the basis of their properties such as melt viscosity, impact strength or tensile strength. These properties are directly dependent on the polymer molecular weight. Tensile strength and impact strength and molecular weight increased. This increase is to some extent, and then it levels out. Polymer melts viscosity, however, show a different trend. In the very high molecular weight, melt viscosity increased more rapidly than the low molecular weight. A commercial polymer should have a low melt viscosity, easy processing of permits, but at the same time, should show good strength.2 Service performance and environmental behaviour of polymersP16.3.1 identify the degradative influences on natural rubber and polypropene Thermal degradation of polymers is molecular deterioration as a result of overheating. At high temperatures the components of the long chain backbone of the polymer can begin to separate and react with one another to change the properties of the polymer. Thermal degradation can present an upper limit to the service temperature of plastics as much as the possibility of mechanical property loss. Indeed unless correctly prevented, significant thermal degradation can occur at temperatures much lower than those at which mechanical failure is likely to occur. The chemical reactions involved in thermal degradation lead to physical and optical property changes relative to the initially specified properties. Thermal degradation generally involves changes to th