Determination of the Stereochemistry of Poly(1,3-cyclohexadiene) via End Group Functionalization

Ward

2005

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The synthesis of trimethoxysilane end-capped linear polystyrene (PS) and star-branched PS and subsequent silicon (Si) surface modification with linear and star polymers are described. Trimethoxysilane terminated PS was synthesized using sec-butyl lithium initiated anionic polymerization of styrene and subsequent end-capping of the living anions with p-chloromethylphenyl trimethoxysilane (CMPTMS). 1 H and 29 Si NMR spectroscopy confirmed the successful end-capping of polystyryllithium with the trimethoxysilane functional group. The effect of a molar excess of end-capper on the efficiency of functionalization was also investigated, and the required excess increased for higher molar mass oligomers. Acid catalyzed hydrolysis and condensation of the trimethoxysilane end-groups resulted in star-branched PS, and NMR spectroscopy and SEC analysis were used to characterize the star polymers. This is the first report of core-functionalized star-shaped polymers as surface modifiers and the first comparative study showing differences in surface topography between star and linear polymer modified surfaces. Surface-sensitive techniques such as ellipsometry, contact angle goniometry, and AFM were used to confirm the attachment of star PS, as well as to compare the characteristics of the star and linear PS modified Si surfaces. The polymer film properties were referenced to polymer dimensions in dilute solution, which revealed that linear PS chains were in the intermediate brush regime and the star-branched PS produced a surface with covalently attached chains in the mushroom regime. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: [3655][3656][3657][3658][3659][3660][3661][3662][3663][3664][3665][3666] 2005

Section: Introductionmentioning

confidence: 97%

Silicon surface modification with trialkoxysilyl‐functionalized star‐shaped polymers

Viswanathan

Ward

2005

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“…The deconvoluted peak from 3.15 to 3.60 ppm was assigned as the epoxidized form of the 1,2‐unit of PCHD, and the peak from 2.80 to 3.15 ppm was assigned to the epoxidized form of the 1,4‐unit of PCHD. The relative values of 1,2‐addition versus 1,4‐addition in the PCHD precursor was shown previously to be approximately 70/30 30. The 13 C NMR analysis of both PCHD and epoxidized PCHD are shown in Figure 5.…”

Section: Resultsmentioning

confidence: 53%

Oxidation and epoxidation of poly(1,3‐cyclohexadiene)

Williamson

Mather

2002

Poly(1,3-cyclohexadiene) (PCHD) derivatives were synthesized via facile chemical modification reactions of the residual double bond in the repeat unit. The oxidation and degradation of PCHD was investigated to enable subsequent controlled epoxidation reactions. PCHD exhibited a 15% weight loss at 110°C in the presence of oxygen. The oxidative degradation, demonstrated by gel permeation chromatography (GPC) and 1 H NMR spectroscopy, was attributed to main-chain scission. Aldehyde and ether functional groups were introduced into the polymer during the oxidation process. PCHD was quantitatively epoxidized in the absence of deleterious oxidation with meta-chloroperoxybenzoic acid. 1 H and 13 C NMR spectroscopy confirmed that polymers with controlled degrees of epoxidation were reproducibly obtained. Epoxidized PCHD exhibited a glass-transition temperature at 154°C, which was slightly higher than that of a PCHD precursor of a nearly equivalent molecular weight. Moreover, GPC indicated the absence of undesirable crosslinking or degradation, and the molecular weight distributions remained narrow. The thermooxidative stability of the fully epoxidized polymer was compared to that of the PCHD precursor, and the epoxidized PCHD exhibited an initial weight loss at 250°C in oxygen, which was 140°C higher than the temperature for PCHD.

“…In light of the ability to controllably synthesize poly(1,3‐cyclohexadiene) polymers with a range of microstructures, a series of polymers containing a high 1,2‐microstructure and a high 1,4‐microstructure were synthesized over a range of molecular weights. Based on our earlier efforts, the microstructure of these polymers was determined with 1 H NMR spectroscopy 31. Polymers with 80% 1,4‐addition were synthesized with a preformed DABCO/ n ‐BuLi initiator adduct at 25 °C in cyclohexane.…”

Section: Resultsmentioning

confidence: 99%

Influence of tertiary diamines on the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene)

Williamson

Kilian

2005

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The living synthesis of poly(1,3-cyclohexadiene) was performed with an initiator adduct that was synthesized from a 1:2 (mol/mol) mixture of N,N,NЈ,NЈtetramethylethylenediamine (TMEDA) and n-butyllithium. This initiator, which was preformed at 65°C, facilitated the synthesis of high-molecular-weight poly(1,3-cyclohexadiene) (number-average molecular weight ϭ 50,000 g/mol) with a narrow molecular weight distribution (weight-average molecular weight/number-average molecular weight ϭ 1.12). A plot of the kinetic chain length versus the time indicated that termination was minimized and chain transfer to the monomer was eliminated when a preformed initiator adduct was used. Chain transfer was determined to occur when the initiator was generated in situ. The polymerization was highly sensitive to both the temperature and the choice of tertiary diamine. The use of the bulky tertiary diamines sparteine and dipiperidinoethane resulted in poor polymerization control and reduced polymerization rates (7.0 ϫ 10 Ϫ5 s Ϫ1 ) in comparison with TMEDA-mediated polymerizations (1.5 ϫ 10 Ϫ4 s Ϫ1 ). A series of poly(1,3-cyclohexadiene-block-isoprene) diblock copolymers were synthesized to determine the molar crossover efficiency of the polymerization. Polymerizations performed at 25°C exhibited improved molar crossover efficiencies (93%) versus polymerizations performed at 40°C (80%). The improved crossover efficiency was attributed to the reduction of termination events at reduced polymerization temperatures. The microstructure of these polymers was determined with 1 H NMR spectroscopy, and the relationship between the molecular weight and glass-transition temperature at an infinite molecular weight was determined for polymers containing 70% 1,2-addition (150°C) and 80% 1,4-addition (138°C).