高分子化学浙江大学polymerMeasurementofratecoefficientsPPT学习教案

1、会计学1高分子化学浙江大学高分子化学浙江大学polymerMeasurementofratecoefficients2第1页/共48页3L0L0+2L0L0+2L0+3L0irradiated by a pulsed laser beam (5-20ns)Monomerphotoinitiator, (solvent & transfer agents)MW of polymer produced by PLP: L0,n=nkpMt0第2页/共48页4第3页/共48页5MRkdtMdRpp1221lnttRkMMp第4页/共48页6A photopolymerizable mixture p

2、asses through a capillary system, is irradiated at a specific location, and polymerizes in the capillary during a well-defined dark period until it drops into a quenching bath with an inhibitor(nitroxyl radicals).Measuring the chain length distribution by size-exclusion chromatography that allows de

3、termination of kp in accordance with the equation.L=kpMt0第5页/共48页7The usual procedure for measuring the chain transfer constant CT involves determination of Xn for a range of T/M values and plotting the data as 1/Xn versus T/M, that is, a Mayo plot. The value of CT is then determined as the straight

4、-line slope of this plot. MTCCRMkkXTMpptn2211第6页/共48页8121tkRRt tpkkttRkMM2/012 0112 tkRRt22RkdtRdtMRkdtMdRpp第7页/共48页9Applying pulsed laser-polymerization (PLP) in conjunction with infrared or near-infrared spectroscopic measurement of monomer conversion induced by a single laser pulse (SP-PLP) allow

5、s for the determination of the ratio of termination to propagation rate coefficients, kt/kp, in wide ranges of temperature; pressure; and monomer conversion. tpkkttRkMM2/012第8页/共48页10Identification and quantification of chain ends are not simple as they give only small signals (relative to the rest

6、of the polymer chain) in a spectroscopic analysis. This can be overcome to some extent by isotopic labeling of the initiator end groups by 14C or by using initiator fragments containing fluorine or phosphorus as NMR-sensitive molecules.The application of the matrix-assisted laser desorption ionizati

7、on time-of-flight mass spectroscopy (MALDI-TOF-MS) to the problem of end-group analysis of polymers brought some promising results to this field of polymerization kinetics. 第9页/共48页11MALDI-TOF-MS第10页/共48页12第11页/共48页13第12页/共48页14第13页/共48页15nStatistical approach (统计方法)nKinetic approach （动力学法）第14页/共48页

8、16第15页/共48页17dttrppRRRRp,a polymer chain with the length n is formed by n-1 propagation steps and one chain stopping (termination or transfer) event of probability (1-p).So the probability of finding a chain of length n is: ppNNnn11number of chains of size ntotal number of chainsnumber-fraction dist

9、ribution第16页/共48页18weight of chains of length n: Wn=mnNnweight of all chains : W=mN0Initial number of monomersMW of monomerppNnNNnNmNmnNWWnnnn11000Since one termination results in one chain, so pNN10211pnpWWnnppNNnn11第17页/共48页1902000400060008000100000246810number fraction (10-4)polymerization degree

10、 p 0.999 0.9995 0.9997504000800012000160000.000.010.020.030.04weight fraction (10-2)polymerization degree p 0.999 0.9995 0.99975第18页/共48页20pNNXn110dttrppRRRRp,1111,kineticndttrpprobnXRRRpXaccording to definition:trdtptrdtptrdtipkineticnRRRRRRRRRRX,)22(212211RMIik第19页/共48页21ppnpNNnXnnn11)1 (1accordin

11、g to calculation:ppppnWWnXnnw11)1 (21221pXXnwpolydispersity index(多分散性指数), PDI第20页/共48页222222)1 ()1 () 1(pnpppnNNnnn There are (n-1) different ways to form a chain of length n from the combination of two chains, so 22211)1 (1pppppnmnm第21页/共48页23322)1 (21ppnWWnnpNNnXnn12ppWWnXnw125 . 121pXXnw22)1 (pn

12、pNNnn第22页/共48页2404000800012000160000.000.010.020.030.04number fraction (10-2)Polymerization degree p 0.999 0.9995 0.9997504000800012000160000.000.010.020.03weight fraction (10-2)polymerization degree p 0.999 0.9995 0.99975Molecular weight distribution curve第23页/共48页25Average molecular weight Disprop

13、ortionation vs CombinationpXn12ppXw125 . 1nwXXpXn11ppXw112nwXX第24页/共48页2602000400060008000100000.000.010.020.030.040.050.06weight fraction (10-2)polymerization degreeXn=1000 disproportionation, p=0.999 combination, p=0.998pXn12pXn11第25页/共48页27第26页/共48页28第27页/共48页291nkknRMRdppSTHG第28页/共48页30enthalpy

14、contribution Hentropy contribution S S is always negative, reflecting the loss of degrees of freedom of the monomer becoming a part of the polymer chain. S is around -105-125 J/(mol*K) for polymerization from R.T. to 100 oC, -TS is around 3042 KJ all chain polymerizations are exothermic. most free-r

15、adical polymerizations are negative with typical values ranging from 30 to 80 kJ/mol. STHGPolymerization is mainly determined by H第29页/共48页31CCCC350 KJ/mol610 KJ/mol2906103502 HSteric effect: -H Resonance effect: -H Styrene(69.9)butadiene(72.8) acrylonitrile (72.4) negative substitute: -H vinyl chlo

16、ride(95.8) vinylidene fluoride(129.7)tetrafluoroethylene(154.8) H bond & solvent: -H acrylic acid(66.9) methacrylic acid(42.3) -第30页/共48页32第31页/共48页33MRTGMRRRTGKRTGGnn1lnlnln01000STHGSHTc1nkknRMRdppeccMRTSTHG1ln00ccMRSHTln0000SHTcM=1.0第32页/共48页34第33页/共48页35For example: H S M at 70 oCkJ/mol J/(molK)M

17、MA 56 1184.3610-3Styrene73 104 2.0910-6-Methylstyrene45 1487.60 001lnSTHRMeeMRTSTHG1ln00equil. monomer concentration第34页/共48页36第35页/共48页37第36页/共48页38第37页/共48页39第38页/共48页40In this mechanism, the dormant chain is dissociated into polymer radical P and capping radical X, where X is assumed to be stable

18、 enough to undergo no reaction other than the combination with P第39页/共48页41第40页/共48页42The dormant chain is activated by the catalytic action of activator A, and the capping agent is transferred to form a stable species AX.第41页/共48页43The dormant chain is attacked by radical P to form the active species P and the dormant species PX. This is an exchange reaction. 第42页/共48页44第43页/共48页45SSSRRSZSRSZSSZSmonomercomonomerSSSSSSmonomercomonomerSHaminedithioestertrithiocarbonateWhat will happen if cyclic dithioester or trithiocarbonate is used?AB block polymerABAblock copolymerA