Synthesis of an (AB)4-type Star Block Copolymer of L-lactide and Cyclohexene Oxide from a Tetra-Arm Telechelic Macrophotoinitiator

Year 2018, Volume: 5 Issue: 3, 1105 - 1118, 01.09.2018

Zafer Uyar , Emel Kaya

https://doi.org/10.18596/jotcsa.450986

Cited By: 1

Abstract

A
multi-step reaction process was applied for the synthesis of a novel and
well-defined star-shaped telechelic macrophotoinitiator with four
poly(L-lactide) (PLLA) arms bearing photoinitiating benzoin groups at the chain
ends (PLLA-PI)₄. To achieve this,
2,2-bis(hydroxymethyl)-1,3-propanediol was used as the initiator which
constitutes the core of the star-shaped polymeric scaffold. Benzoin
photoreactive end groups of the telechelic (PLLA-PI)₄, capable of
entering into further polymerization, allowed its use as a prepolymer in
photoinduced free radical promoted cationic polymerization with cyclohexene
oxide (CHO) monomer at l=350 nm to produce an (AB)₄-type
star-shaped block copolymer composed of both esteric L-lactide and etheric
cyclohexene oxide chains on each arm, (PLLA-PCHO)₄.
Structural analysis and characterization of all intermediate and final
compounds were done by a series of analytical and spectral methods. Molecular
weights of the prepared polymers up to telechelic macrophotoinitiator (PLLA-PI)₄
were determined based on ¹H-NMR (M_n
H-NMR), GPC (M_{n exp})
analyses and theoretical calculations (M_n
theo) and were found to be in good agreement with each other. The thermal
behaviors of the polymers synthesized were investigated by thermogravimetric
and differential thermal analysis (TG/DTA). The melting temperature for
(PLLA-PCHO)₄ was found higher compared to the other homo-type
polymers in the literature. The thermogravimetric (TG) analyses showed that
introduction of the thermally stable PCHO segment into the structure via
photopolymerization increased its stability shifting its decomposition
temperature to the higher values compared to the prepolymers.

Keywords

Poly(L-lactide), ring opening polymerization (ROP), star-shaped telechelic macrophotoinitiator, photoinduced polymerization, star block copolymer

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