Santillo, Chiara
(2017)
A molecular approach to study structure and properties of polymers.
[Tesi di dottorato]
| Item Type: |
Tesi di dottorato
|
| Resource language: |
English |
| Title: |
A molecular approach to study structure and properties of polymers |
| Creators: |
| Creators | Email |
|---|
| Santillo, Chiara | chiara.santillo@unina.it |
|
| Date: |
10 April 2017 |
| Number of Pages: |
260 |
| Institution: |
Università degli Studi di Napoli Federico II |
| Department: |
Scienze Chimiche |
| Dottorato: |
Scienze chimiche |
| Ciclo di dottorato: |
29 |
| Coordinatore del Corso di dottorato: |
| nome | email |
|---|
| Paduano, Luigi | luigi.paduano@unina.it |
|
| Tutor: |
| nome | email |
|---|
| DE ROSA, CLAUDIO | UNSPECIFIED | | AURIEMMA, FINIZIA | UNSPECIFIED |
|
| Date: |
10 April 2017 |
| Number of Pages: |
260 |
| Keywords: |
crystalline block-copolymers; crystal structure; polymorphism |
| Settori scientifico-disciplinari del MIUR: |
Area 03 - Scienze chimiche > CHIM/04 - Chimica industriale |
[error in script]
[error in script]
| Date Deposited: |
03 May 2017 17:23 |
| Last Modified: |
14 Mar 2018 10:06 |
| URI: |
http://www.fedoa.unina.it/id/eprint/11802 |
| DOI: |
10.6093/UNINA/FEDOA/11802 |
Collection description
In this thesis were studied the structure and the physical properties of novel materials prepared with different synthetic strategies aimed at producing the desired molecular structure:
1. Organometallic catalysts for polymerization of dienes to stereoregular polydienes and successive hydrogenation for producing polyolefins and copolymers with novel molecular architectures;
2. Organometallic non-metallocene catalysts for producing semicrystalline block copolymers;
All research topics are pursued with the main aim to exploit the concept of retro-design of the physical properties, that is, to identify the best molecular architecture, synthetic approach, and processing conditions that ensure to obtain the target tailored properties.
Regarding the first topic the crystals structures of isotactic 1,2-poly((E)-3-methyl-1,3-pentadiene) (iP3MPD12) and isotactic poly((R,S)-3-methyl-1-pentene) (iP(R,S)3MP) have been determined by analysis of the X-ray powder and fiber diffraction patterns and conformational and packing energy calculations. The iP3MPD12 has been synthesized with the catalytic system CoCl2(PnPrPh2)2/MAO and is one of the very few examples of crystalline isotactic 1,2-polydienes described in the literature. From the successive hydrogenation of iP3MPD12 a novel isotactic poly((R,S)-3-methyl-1-pentene), characterized by a random enchainment of R- and S-3-methyl-1-pentene, has been obtained. The crystal structure analysis has revealed that iP3MPD12 is characterized by chains in 7/2 helical conformation packed in an orthorhombic unit cell with axes a = 17.4 Å, b =16.5 Å, c = 15.3 Å according to the space group P21ab.
The hydrogenated polymer of iP(R,S)3MP is instead characterized by chains in 4/1 helical conformation packed in in a monoclinic unit cell with parameters a = 10.02 Å, b = 18.48 Å, c = 6.87 Å, and γ = 109.9° according to the space group P21/b or P21. A high degree of disorder is present in the crystals due to the random enchainment of the enantiomeric R and S monomeric units, whose chirality influences the handedness of the helical chains and the conformation assumed by the lateral groups. The crystal structure of iP(R,S)3MP is different from the tetragonal structure of the pure enantiomer iP(S)3MP. This is due to different entropic effects, related to the presence of different types of disorder included in the crystals that drive crystallization in different packing modes. The crystal structure of iP(R,S)3MP provides an example of the effect of the chirality of side groups on the crystal packing and is an example of symmetry breaking in the structures of polymers.
In the second part of this thesis the structure, the morphology and the physical properties of crystalline-crystalline diblock copolymers synthesized with living, stereospecific polymerization using an Hf-based post-metallocene catalyst have been investigated. Samples of isotactic polypropylene-block-polyethylene (iPP-b-PE) and isotactic polypropylene-block-linear low density polyethylene (iPP-b-LLDPE), of different block lengths have been prepared and characterized.
The influence of the molecular architecture, in terms of molecular mass, different block lengths and composition, on the crystallization behavior, morphology and mechanical properties of these systems has been studied. This analysis has shown that the physical properties of these crystalline block copolymers can be easily tailored by controlling the molecular parameters, and conditions of crystallization.
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